The present invention relates to a reciprocating piston type refrigerant compressor adapted for use in an automotive air conditioning system.
For compressing refrigerant gas for an automotive air conditioning system, various kinds of piston compressors are available, including double-headed and single-headed piston types in respect of the piston configuration, and constant and variable capacity types in terms of the piston drive mechanism. Generally, these different compressors have a cylinder block in which a plurality of cylinder bores are formed for receiving therein reciprocally slidable pistons, and a pair of housings which are disposed so as to close the opposite axial ends of the cylinder block, and these housings and the cylinder block are fastened together by means of a plurality of common through bolts extending through these parts.
In a typical swash-plate type compressor equipped with double-headed pistons as shown in FIG. 3 in longitudinal cross section, the opposite ends of cylinder block means of the compressor formed by a pair of cylinder block members 1a, 1b are closed by front and rear housings 2, 3 and these four members 1a, 1b, 2, 3 are fastened together by means of a plurality of through bolts 10 (only one bolt being shown in FIG. 3). Referring now to FIG. 4 showing a typical wobble-plate, variable-displacement type compressor with single-headed pistons, its cylinder block 1 and the front and rear housings 2, 3 closing the opposite axial ends of the cylinder block 1 are also tightened together similarly by means of a plurality of bolts 10, while the through bolts 10 are usually made of a ferrous metal.
In view of the application of the compressors to an automotive air conditioning system, at least the pair of housings 2, 3 are usually made of an aluminum alloy for the sake of lightweightness of the compressors.
In a compressor constructed such that the bolts 10 pass through part of the gas passage in the compressor, e.g. swash plate chamber 4a and suction passage 4b in FIG. 3 or a crankcase chamber 4 in FIG. 4, a bore 6 formed in the front housing 2 for receiving therein one shank end portion of the bolt 10 adjacent its head forms with the bolt shank an annular clearance which is in direct communication with the gas passage in the compressor. For this reason, provision must be made to seal the opening of the bolt receiving bore 6 adjacent the bolt head while the tightening force of the bolt is retained. For this purpose, a washer 5 which is made of, e.g., a copper alloy is disposed between the head of the bolt 10 and a bearing surface formed on the front housing 2 so that the bolt head is supported by the bearing surface by way of the washer 5. It is to be noted, however, that the tightening force of the bolt 10 is built up with an increase in the temperature of the compressor in its continued operation because the housings 2, 3 made of aluminum alloy expand greater extent than the bolts 10 made of ferrous metal having a smaller linear expansion coefficient than the aluminum alloy. Such increased tightening force of the bolt acting on the housing may cause its bearing surface to be buckled or collapsed particularly at the inner edge region thereof adjacent the opening of the bolt receiving bore 6, as indicated by Z in FIG. 2. Such damage to the bearing surface reduces the tightening force of the bolt, thereby causing development of noise and vibration and also affecting gas sealing at the washer 5.
An object of the present invention, which is made in light of the above-described drawback, is to provide a refrigerant compressor which can prevent the tightening forces of the bolts from being reduced and also ensure fluid-tight sealing.